Common medications linked to adverse breast cancer outcomes

An international study involving 23,000 people has found concerning evidence about the impact of a range of common medications on the treatment outcomes for patients with breast cancer.

Led by the University of South Australia (UniSA) and Flinders University, researchers investigated how everyday items such as blood pressure tablets, cholesterol-lowering drugs and heartburn medication may interact with cancer therapies. The data was based on 19 major clinical trials sponsored by pharmaceutical companies including Lilly, Pfizer and Roche, and is believed to be the largest and most comprehensive analysis of its kind in the world.

Published in the journal Cancer Medicine, the study found that proton pump inhibitors (PPIs) used to treat indigestion and heartburn were associated with poorer overall survival for patients with breast cancer, as well as a 36% higher risk of severe, treatment-associated side effects. It is thought that proton pump inhibitors may interfere with the body’s immune responses or alter how cancer drugs are absorbed and metabolised, although further investigation is needed.

The study also found that beta blockers, ACE inhibitors, angiotensin receptor blockers and calcium-channel blockers — drugs commonly prescribed for heart disease or hypertension — were linked to higher rates of severe side effects. However, these medications did not appear to affect overall survival.

Statins and metformin — frequently used to manage high cholesterol and diabetes respectively — meanwhile showed no significant impact on either survival or adverse events, offering reassurances about their safety.

Lead author Dr Natansh Modi, from UniSA and Flinders University, said the findings reveal a complex relationship between commonly prescribed medications and cancer outcomes.

“Many women with breast cancer are also managing other chronic conditions such as high blood pressure, diabetes or acid reflux, meaning they are often taking multiple drugs at once,” Modi said.

“Our results don’t suggest that people should stop taking their non-cancer medicines, but it underlines how important it is for doctors to regularly review patient medications, because people are living longer and managing multiple health issues.”

Flinders University Associate Professor Ashley Hopkins, corresponding senior author on the study, said the findings show that patients taking PPIs in oncology settings warrant closer attention in particular.

“It doesn’t mean that patients should cease their reflux medication without medical advice, but clinicians should be alert to potential risks and review whether PPIs are genuinely needed,” he said.

According to the researchers, the study highlights the need for a more holistic approach to breast cancer management that considers all medications that a patient is taking. They are now calling for follow-up studies to explore the biological reasons behind the observed drug interactions and to develop clinical guidelines for the safe co-prescription of these medicines during cancer therapy.

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